Radiosurgery x-ray system with collision avoidance subsystem

ABSTRACT

A method for preventing an emission head or arm assembly from entering an exclusion zone. The method may include calculating a variable dimension exclusion zone of a radiosurgery system, and preventing at least one of the emission head or arm assembly from entering the variable dimension exclusion zone. The method may also include establishing a exclusion zone of a radiosurgery system, the radiosurgery system comprising an x-ray source having an emission head, moving the emission head during treatment of a patient, wherein the exclusion zone travels with the emission head, and detecting a presence and location of an object in the traveling exclusion zone.

RELATED APPLICATIONS

This application claims the benefit of U.S. application Ser. No.10/814,451, filed Mar. 31, 2004.

TECHNICAL FIELD

The present invention relates to radiosurgery and radiotherapy.

BACKGROUND

In radiosurgery, very intense and precisely focused doses of radiationin a beam from a source outside a patient's body are delivered to atarget region in the body, in order to destroy tumorous cells.Typically, the target region consists of a volume of tumorous tissue.Radiosurgery requires an extremely accurate spatial localization of thetargeted tumors. Radiosurgery offers obvious advantages overconventional surgery, during which a surgeon's scalpel removes thetumor, by avoiding the common risks and problems associated with opensurgery. These problems include invasiveness, high costs, the need forin-hospital stays and general anesthesia, and complications associatedwith post-operative recovery. When a cancerous tumor is located close tocritical organs, nerves, or arteries, the risks of open surgery are evengreater.

As a first step in performing radiosurgery, it is necessary todeteIn1ine with great precision the location of tumors and anysurrounding critical structures, relative to the reference frame of thetreatment device. CT and MRI scans enable practitioners to preciselylocate a tumor relative to skeletal landmarks or implanted fiducialmarkers. However, it is also necessary to control the position of theradiation source so that its beam can be precisely directed to thetarget tissue, with control of propagation in and through other bodystructures.

To effect such beam position control, stereotactic frames have beendeveloped and used in the past for treatment of brain tumors.Stereotactic frames are rigid metal frames that are attached to thepatient's skull and locked in place to provide a frame of reference forthe surgeon during CT/MRI imaging, and for subsequent therapeutictreatment. A stereotactic frame is typically attached to the patientprior to scanning/imaging. The frame must remain in place while thesurgeon is developing a computerized treatment plan, as well as duringthe actual treatment. During treatment, an x-ray or gamma ray source isprecisely positioned with respect to the frame, so that the radiationcan be administered according to the treatment plan.

While there are well-developed methods for attaching stereotactic framesto the skull for brain tumor treatment, attaching these frames toanatomical regions other than the skull in order to establish a stableframe of reference is too difficult to be practical. As one prior artexample, a stereotactic frame that was deliberately constructed for therest of the body (outside the head/neck region) required screws to beplaced in the pelvis, incisions to be made along the spine toaccommodate spinal clamps, and ten hours of general anesthesia to beadministered to the patient while the frame was being attached to thepatient, CT imaging performed, and radiosurgery undertaken. It isclearly not practical to perform such frame-based radiosurgery on areasother than the skull, and therefore the use of frame-based radiosurgeryhas so far been restricted to the treatment of intra-cranial tumors.

Despite the advantages of radiosurgery over open surgery, includingsignificantly lower cost, less pain, fewer complications, no infectionrisk, no general anesthesia, and shorter hospital stays (mostradiosurgical treatments are outpatient procedures), frame-basedradiosurgery has a number of drawbacks. These drawbacks mostly relate tothe use of the stereotactic frame. A stereotactic frame causes pain tothe patient, since it has to be attached with screws. Also, a framecannot be easily re-attached in precisely the same position for asubsequent radiation procedure, so that frame-based radio surgicaltreatment is limited to smaller tumors (generally less than about threecentimeters in diameter) that can be treated in a single procedure.Moreover, the frame must remain in place from the time of diagnostic CTand/or MRI scanning, through the entire period of treatment, which mayextend over a multi-day period. Finally, the biggest drawback is thatframe-based radiosurgery cannot be used for tumors located outside ofthe head and neck region, because of the above-described difficulty ofattaching these frames to anatomical regions other than the skull.Frame-based radiosurgery therefore cannot be used to treat ninetypercent of all solid tumors, because they occur outside of the head/neckregion.

These drawbacks have lead to the development of a frameless stereotacticradiosurgery system, exemplified by the CyberKnife system (henceforth“CyberKnife”) made by Accuray, Inc., Sunnyvale, Calif. CyberKnife is animage guided robotic system which eliminates the need for the rigidstereotactic frames described above, and enables the treatment ofextra-cranial tumor sites. CyberKnife provides numerous advantagescompared to conventional stereotactic radiosurgery systems, includingbut not limited to: ability to treat tumors throughout the body, notjust those located within the head/neck region; increased access to, andcoverage of, any target volume; ability to treat tumors that are largerthan about three centimeters in diameter; minimal constraints on patientset-up; ability to deliver a plurality of fractionated treatments; andenhanced ability to avoid damaging critical structures.

CyberKnife includes a robotic system onto which an x-ray linearaccelerator (“linac”) is mounted, and a controller. The linac is adaptedto selectively provide a precisely shaped and timed radiation beam. Thecontroller uses CT and possibly MRI data, or other types of image data,that define the target tissue and important other bodily structures,together with treatment planning and delivery software to identify aseries of landmarks within the treatment region, prior to surgery.CyberKnife may further include a stereo x-ray imaging system, whichduring treatment repeatedly measures the 10cation and orientation ofthese landmarks relative to the linac. Prior to the delivery ofradiation at each delivery site, the controller directs the roboticsystem to adjust the position and orientation of the linac in accordancewith the measurements made by the x-ray imaging system, so that adesired series of radiation beams can be applied to the body, optimallydosing the target tissue while minimizing radiation to other bodystructures. In this way, CyberKnife allows accurate delivery of highdoses of radiation, without requiring a stereotactic frame.

It is important to ensure that during the successive positionings of thelinac during a treatment, the robotic system does not collide withobjects (for example, parts of the patient's body, its own structure, orother equipment in the treatment room). Since patient setup is minimallyconstrained by a frameless radiosurgery system, it is difficult to havecomplete knowledge of the patient's body position when preparing atreatment plan, particularly regarding their arms and legs. An obstacledetection/collision avoidance system would therefore be desirable inframeless radiosurgery systems such as the CyberKnife,

Because of its ability to deliver fractionated treatments, CyberK11ifeis well adapted for radiotherapy, as well as for radiosurgery. The termradiotherapy refers to a procedure in which radiation is applied to atarget region for therapeutic, rather than necrotic, purposes. Theamount of radiation utilized in radiotherapy is typically about an orderof magnitude smaller, as compared to the amount used in radiosurgery.Radiotherapy is frequently used to treat early stage, curable cancers.In addition to delivering radiation to cancerous tissue, radiotherapysystems generally also irradiate a certain amount of normal tissuesurrounding the tumor. Typically, a series of relatively small doses aredelivered over a number of days. Each radiation dose not only kills alittle of the tumor, but also creates some collateral damage to healthysurrounding tissue, which however usually heals by itself, because ithas a greater ability to repair, compared to cancerous tissue.

A collision avoidance system, referred to above, would also be desirablewhen CyberKnife is being used for radiotherapy, as well as forradiosurgery. For convenience, the term “radiosurgery” in thisapplication shall henceforth mean “radiosurgery and/or radiotherapy.”

The present invention provides a frameless radiosurgery system having acollision avoidance subsystem.

In an exemplary embodiment, a frameless radiosurgery system inaccordance with the present invention includes an x-ray source, and arobot. The robot includes an arm assembly extending from a base unit.The x-ray source, which in a preferred form is a linac, has an emissionhead mounted at a distal end of the arm assembly. The x-ray emissionhead is adapted for selectively emitting an x-ray beam along a beamaxis. The arm assembly may be articulated (i.e., have a series of rigidelements linked by rotatable couplings), may be flexible (i.e., have aseries of rigid or flexible elements linked by flexible couplings), ormay be a combination of both articulated and flexible portions.

The radiosurgery system further includes an associated controller forselectively orienting the x-ray emission head whereby the x-ray beamextends along a succession of treatment axes. The radiosurgery systemfurther includes a collision avoidance subsystem, including means forpreventing the x-ray emission head and the arm assembly from effecting acollision with an object in one or more pre-defined exclusion zones.

In one exemplary embodiment of the invention, the collision avoidancesubsystem includes a light source (such as a laser or an LED(light-emitting-diode) effective to establish a substantially planar (orsheet-like) light beam between the exclusion zone and the emission head.The planar light beam may be fan-shaped. In this embodiment, thecontroller is responsive to observation of an object extending throughthe light beam, to interrupt any further motion of the head toward theexclusion zone. The light source may be fixedly positioned with respectto the x-ray emission head, defining an exclusive zone that “travels”with the head. Alternatively, the light source may be fixedly positionedwith respect to the base unit of the robot, for example by being mountedon a wall of the treatment room, defining an exclusive zone that isfixed with respect to the treatment room.

In another embodiment of the invention, the collision avoidancesubsystem includes a least one optical emitter-receiver pair that iseffective to detect the breaking of a light beam when an object extendsinto the one or more exclusion zones. The optical emitter is a lightsource, as described in paragraph 15 above. The optical receiver isconstructed and arranged to receive light that 1) has reached an objectthat has intruded into one or more of the exclusion zones, and 2) isback-scattered from the object.

In another embodiment of the invention, the collision avoidancesubsystem includes a laser range finder that can detect movement of anobject into a light beam. The laser rangefinder includes a transmitterthat generate laser light and transmits the light toward one or moreexclusion zones, and a receiver/photodetector for receiving anddetecting laser light that is backscattered from any object thatintrudes into the one or more exclusion zones. The laser range finderincludes means for determining, from the received back-scattered laserlight, the distance to the object.

In another embodiment of the invention, a plurality of exclusion zonesmay be defined. In other words, multiple “layers” of exclusion zones maybe defined. In one of many possible exemplary embodiments, a first“shell-like” exclusion zone may be defined which slows down the motionof the head. In this exemplary embodiment, a second exclusion zone maybe defined, which completely stops any further motion of the head, whenthe head reaches one or more boundaries between the first exclusion zoneand the second exclusion zone. In another embodiment of the invention,at least one of the exclusion zones is not a static zone, but rather isa variable dimension exclusion zone. In another embodiment of theinvention, the collision avoidance subsystem includes an array ofacoustic transducers fixedly coupled to the x-ray emission head. Each ofthe transducers transmits a succession of acoustic pulses along atransmission axis extending from the head, and detects acoustic energybackscattered along the transmission axis from an object disposed alongthe transmission axis. The beam axes are mutually aligned wherebycross-sections of adjacent pairs of the pulses transverse to thetransmission axis are contiguous at a predetermined distance from thehead. In this embodiment, the collision avoidance subsystem includesmeans for determining, from the received backscattered acoustic energy,the distance between the head and the object.

The collision avoidance subsystem further includes means forinteJ11lpting, in response to the determined distance being at or lessthan a predetermined value, any further motion of the head toward theexclusion zone.

In another embodiment of the invention, the collision avoidancesubsystem includes a sensor disposed on a surface of the articulated armassembly. The sensor is operative to generate an alarm signal uponimpact of the sensor with an object, during motion of the arm assemblyand/or the x-ray emission head. The subsystem further includes meansresponsive to the alaIn1 signal to interrupt any further motion of thearm and/or head. The sensor may be a tactile sensor, or other type ofsensor adapted for proximity sensing. By way of example, the sensor mayconsist of a fluid-filled bladder, and a pressure transducer coupled tothe bladder, in one embodiment of the invention. In other embodiments,the sensor may be an infrared (IR) sensor, or an electrostaticcapacitance sensor.

In any of the above described collision avoidance systems, the detectionof breach of the exclusion zone and the system's response to suchdetection may be automatic (e.g., under control of the controller) ormay be manually implemented (e.g., when a human observer detects abreach, that observer initiates the system response (e.g., haltingfurther advance of the head).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1 illustrates a frameless stereotactic radiosurgery system known inthe prior art.

FIG. 2 illustrates a frameless stereotactic radiosurgery x-ray systemincluding a collision avoidance subsystem, constructed in accordancewith an exemplary embodiment of the present invention.

FIG. 3A illustrates a collision avoidance subsystem, in which a lightsource is fixedly positioned with respect to the base unit of a robotthat manipulates the position of the x-ray linac.

FIG. 3B illustrates a collision avoidance subsystem, in which a lightsource is fixedly positioned with respect to the x-ray emission head ofan x-ray linac.

FIG. 4 illustrates a collision avoidance subsystem, constructed inaccordance with another embodiment of the present invention, andincluding an array of acoustic transducers.

FIG. 5A illustrates an array of four ultrasonic transducers, arrangedabout an x-ray emission head in a rectangular pattern.

FIGS. 5B and 5C illustrate sense cones formed by the ultrasonictransducers shown in FIG. 5A.

FIG. 6 illustrates a collision avoidance subsystem, constructed inaccordance with another embodiment of the present invention, andincluding a tactile sensor.

DETAILED DESCRIPTION

The present invention provides a frameless radiosurgery system includingan x-ray source and an associated robot positioning system and acollision avoidance subsystem. The collision avoidance subsystemprevents the x-ray source, the robot system, or components of the robotsystem, from colliding with any critical components (for example thepatient, or parts of the radiosurgery system, or other equipment).

FIG. 1 illustrates a frameless stereotactic radiosurgery (and/orradiotherapy) system 10 known in the art. An exemplary radiosurgery(and/or radiotherapy) x-ray system is described in commonly-owned U.S.Pat. No. 5,207,223 and in commonly-owned U.S. Pat. No. 5,427,097.

In overview, the radiosurgery system 10 includes: a robot system 12,having a fixed base and including an articulated arm assembly; aradiation source 14 mounted at the distal end of the articulated armassembly; a stereo x-ray imaging system 16; and a controller 18. Theradiation source 14 is preferably an x-ray linear accelerator (“linac”).The stereo x-ray imaging system 16 typically consists of a pair of x-raysources 17, and a pair of x-ray image detectors 21, each detector beingopposite an associated one of x-ray sources 17. The controller 18contains treatment planning and delivery software 20, which isresponsive to CT and/or MRI data and user input to generate a treatmentplan consisting of a succession of desired beam paths, each having anassociated dose rate and a duration at each of a fixed set of nodes. Inresponse to the controller's directions, the robot 12 moves (andorients) the x-ray source and controls beam intensity, successively andsequentially through each of the nodes, while delivering the associateddose.

FIG. 2 illustrates a frameless stereotactic radiosurgery x-ray system100 that is similar to system 10 but further includes a collisionavoidance subsystem 200, constructed in accordance with an exemplaryembodiment of the present invention. In overview, the radiosurgery x-raysystem 100 in the illustrated embodiment includes a robot system 102; aradiation source 104; an x-ray imaging system 106; a controller 108; anda collision avoidance subsystem 200. A patient positioning table 122 maysupport the patient relative to the x-ray imaging system 106 and otherequipment. Once in position, the position table 122 remains fixedthroughout the treatment.

Typically, the robot system is an industrial robot/manipulator 102. Forexample, a Fanuc 420 or Kuka 210 may be used. In the preferred form, therobot system 102 includes an articulated arm assembly 112 extending to adistal end 113 from a base unit 114, affixed to the floor of thetreatment room. The radiation source 104 is mounted at the distal end113 of the arm 112.

Preferably, the radiation source is a small x-ray linac (linearaccelerator) 104. Typically, the linac 104 includes a waveguide, throughwhich microwave radiation is fed in, so as to accelerate electrons. Theelectrons may be produced by a pulsed electron gun, by way of example.The linac 104 includes an x-ray emission head 105 adapted forselectively emitting an x-ray beam 120 along abeam axis 121. The linac104 also includes a collimator 107 for collimating the x-ray beam 120,before the beam 120 is delivered to the desired treatment region. Thelinac 104 typically weighs about 100 kg, although other weight rangesare also within the scope of the present invention.

The x-ray imaging system 106 may include two x-ray sources 124 mountedto the ceiling of the treatment room, and a pair of x-ray imagedetectors 126 mounted orthogonally, typically on the floor. Each of thedetectors 126 is opposite an associated one of x-ray sources 124. Thex-ray image detectors 126 may be amorphous silicon image detectors orcameras.

The controller 108 includes the software operating system for theframeless radiosurgery system 100. The controller 108 may be a dualprocessor computer, which performs numerous functions, including but notlimited to: 1) performing treatment planning: 2) providing 3-D displaysof images (e.g., from x-ray data); 3) calculating the requisite dose ateach desired node; 4) controlling the x-ray linac and the robotic arm;5) managing and recording the treatment; and 6) monitoring the equipmentfor patient safety.

Before the radiosurgery treatment, a CT scan is taken of the tumorregion, i.e. of the portion of the patient's anatomy that contains thetumors of interest. A set of digitally reconstructed radiographs (DRRs)are generated for the tumor region, based on the pre-operative CT scan.DRRs are artificial, synthesized 2D images that represent the

shadow graphic image of the tumor that would be obtained, if imagingbeams were used having the same intensity, position, and angle as thebeams used to generate real time radiographic images of the tumor, andif the tumor were positioned in accordance with the 3D CT scan.

The image detectors 126 then obtain live (“real-time”) radiographicimages, by capturing x-ray images from the ceiling-mounted x-ray sources124. The controller 108 correlates these live radiographic images withthe pre-computed array of synthetic radiographs, and directs the robot102 to adjust the position of the linac 104 accordingly.

In other words, patient location and movement is tracked by the matchingthe “live” x-ray images to the pre-computed set of synthetic images thatcorrespond to various projected movements of the patient. Standard imageprocessing techniques are used to subtract the images and obtain ameasure of the differences between the images.

The resulting imaging information is transferred to the robot 102 by thecontroller 108, which directs the robot 102 to compensate for anychanges in patient position by repositioning the linac 104. Under thedirections of the controller 108, the articulated arm assembly 112manipulates the linac 104 in order to accommodate tumor movement, causedby patient movement. In this way, the controller 108 selectively orientsthe emission head 105 of the linac 104, whereby the emitted x-ray beamextends along a succession of treatment axes, in order to destroy tumorslocated within the pre-scanned treatment region. The treatment axes aredisposed in a patient zone surrounding the patient.

While the articulated arm assembly 112 of the robot 102 moves around inorder to adjust the position of the linac 104, in response to directionsfrom the controller 108, it is important to prevent any part of therobotic system 102, and the linac 104, from colliding with other objectsin the treatment room. These objects may include, but are not limitedto, other parts of the patient's body, and other equipment such as thepatient positioning system. As just one example, in a radiosurgerysession for treating tumors in the stomach, it is desirable to preventthe x-ray linac 104 or the arm assembly 112 from colliding with the headof the patient, while the arm assembly 112 is maneuvering the x-ray beaminto a correct position.

Accordingly, in one form, the present invention features a collisionavoidance subsystem 200 for detecting, and responding to, the relativepassage of the x-ray source or any part of the robot system 102 into apredefined exclusion zone 140. In this form of the invention, theexclusion zone 140 is fixed relative to, and surrounds (at least inpart) the patient. In another form of the invention, a predefinedexclusion zone 140 is fixed with respect to, and travels with, theemission head (the x-ray source). In this form, collision detectionsubsystem 200 detects, and responds to, relative passage of any object(e.g., the patient or equipment or any other object) into the exclusionzone. In both forms, the collision avoidance system 200 preventscollision of any part of robot system and/or x-ray source with anyobject in the exclusion zone 140. In one embodiment, the collisionavoidance system 200 detects intrusion of an object into the exclusionzone 140 and upon such detection, prevents or slows down furtherrelative advance of such object in the exclusion zone.

In one embodiment, the collision avoidance system 200 is effective toprevent the radiosurgical (or radiotherapeutic) x-ray head itself fromentering the exclusion zone(s), instead of preventing the collisionbetween an object and any part of the robot system and/or x-ray sourcewithin the exclusion zone.

In the present invention, in order to establish an exclusion zone, acomputer-aided design (CAD) model of the room used for radiosurgerytreatment is set up by the operating system in the controller 108, priorto treatment. During set-up of the CAD model of the treatment room, theexclusion zone 140 is computed by the treatment planning software in thecontroller 108. The exclusion zone 140 defines a region surrounding thepatient within which neither the x-ray linac 104 nor the articulated armassembly 112 of the robot system 102 may enter. A number of parametersmay be used in the computation of the exclusion zone 140, including butnot limited to: the size and dimensions of the patient; the expectedmovements of the patient during treatment; and the location of thepatient positioning system 122. This exclusion zone can be updated inreal time by feedback from, for instance, the patient positioning system122.

In an exemplary embodiment of the invention (not illustrated), more thanone exclusion zone may be computed and defined. In other words, aplurality (or multiple “layers”) of exclusion zones may defined. In justone of many possible examples and variations, a first “shell-like”exclusion zone may be defined in which the motion of the head is sloweddown, but not completely halted. A second exclusion zone may be defined,which completely stops any further motion of the head, when the headreaches the boundary between the first exclusion zone and the secondexclusion zone.

In an embodiment of the invention illustrated in FIG. 3A, the collisionavoidance subsystem 200 uses one or more light sources to define theexclusion zone 140. In this embodiment, the one or more light sourcesare effective to establish a set of substantially planar (or sheet)light beams between the pre-computed exclusion zone 140 and the x-rayemission head 105 of the linac 104, by sweeping one or more linear lightbeams into substantially planar pattern light beams. In the illustratedembodiment, one or more light sources are fixedly positioned withrespect to the base unit 114 of the robotic system 102. For example, thelight sources may be mounted to a wall of the treatment room. The lightsources establish a substantially planar light beam by sweeping a linearlight beam along a plane.

By way of example, a “rectangular” exclusion zone 140 is illustrated inFIG. 3A.

As shown in FIG. 3A, the exclusion zone 140 is defined by three distinctplanar light beams, 150A, 150B, and IS0C. Each planar light beam extendsfrom a respective one of line sources 160A, 160B, and 160C, mounted tothe wall, where each “line source” is a plurality of light sources(lasers or LEDs) that are lined up to form a “line” of light sources.The principal plane of beam 150A is perpendicular to the principal planeof beam 150B, which is perpendicular to the principal plane of beam150C, establishing an inverted V-shaped channel extending about theexclusion zone 140 and parallel to a patient axis 170 of the exclusionzone 140. The dimensions of the beams 150A, 150B, and 150C are such thata patient lying along axis 170 on a table beneath the zone 140 is whollywithin the zone 140.

In the illustrated embodiment, the beams 1S0A, 150B, and 150C may beformed by a linear array of light sources (such as lasers or LEDs)extending along each of 160A, 160B, and 160C. Alternatively, each of theplanar beams 150A, 1S0B, and 150C may be formed from a single lightsource (such as a laser or an LED) for each beam, which is repetitivelyswept in the principal planes of these beams.

In one embodiment (not illustrated), the collision avoidance systemincludes at least one optical emitter-receiver pair that is capable ofdetecting the breaking of a light beam as the light beam reaches anobject within an exclusion zone, and is scattered off that object. Inthis form of the invention, at least one of the light sources (describedin paragraphs 44-46 above) is provided with a corresponding lightreceiver (not illustrated). The light receiver receives light from alight beam that was generated by the light source (i.e. the “emitter” inthe emitter-receiver pair), then was “broken” by reason of beingincident upon an object extending through one of the exclusion zones,and of being back-scattered by that object. A photodetector may becoupled to the light receiver, to detected the intensity of theback-scattered light.

In another embodiment of the invention (not illustrated), the collisionavoidance subsystem includes a laser rangefinder (or equivalently alidar, an acronym that stands for LIght Detection And Ranging) that candetect movement of an object into a light beam defining the exclusionzone. As known in the art, a laser rangefinder is a laser device thatcan accurately measure the distance to an object by sending out light tothe object and analyzing the light that is reflected/scattered off ofthe object. The range to the object is determined by measuring the timefor the light to reach the object and return.

In this embodiment, the laser rangefinder may include: 1) a transmitterthat generates laser light and transmits the laser light toward one ormore exclusion zones, or toward one or more boundaries of the exclusionzone; 2) a receiver for receiving the transmitted light that isback-scattered from any object that intrudes into the one or moreexclusion zones; 3) a photodetector for detecting the intensity of thelight received by the receiver; and 4) a data acquisition system,effective to compute the distance to the object by making time-or-flightmeasurements, i.e. by measuring the time required for the light to reachthe object and return.

The transmitter includes a laser source for generating laser light. Forexample, a diode-pumped Nd—YAG (neodymium-yttrium-aluminum-garnet) lasermay be used; however, any other commercially available laser source maybe used. The transmitter may also include a light-beam steering unit fordirected the generated laser light towards the desired exclusion zone orboundary thereof. The receiver may be any conventional light receiverthat is commercially available. The photodetector may be aphotomultiplier tube or avalanche photodiode. The data acquisitionsystem may include a time-of-flight electronics unit (including one ormore amplifiers, a clock oscillator, one or more filters, a digitizer,and a demodulator) and a microprocessor controller.

In one form, the transmitter component of the laser range finder may becoupled to the x-ray emission head. In this form of the invention, thetransmitter generates and transmits a laser pulse along a light axisextending from the head, and detects laser light back-scattered alongthe light axis from an object disposed along the light axis. Thereceiver, detector, and data acquisition components of the laserrangefinder determines, from the received backscattered laser light, thedistance between the head and the object. The microprocessor controllerunit may include means for interrupting, in response to the determineddistance being at or less than a predetermined value, any further motionof the head toward the exclusion zone.

In one form, a doppler lidar may be used to measure the velocity of theobject, as the object moves into or within the one or more exclusionzones. When the light transmitted from the lidar hits a target movingtowards or away from the lidar, the wavelength of the lightreflected/scattered off the target is slightly changed. (If the objectis moving away, the return light has a longer wavelength; if the objectis moving closer towards the lidar, the return light has a shorterwavelength.) The doppler lidar is effective to measure the resultingDoppler shift, and hence determine the velocity of the object.

In a manually controlled subsystem 200, the controller 108 is responsiveto a user action, taken in response to observation of an objectextending within the exclusion zone 140, to interrupt any further motionof the x-ray emission head 105 toward the exclusion zone 140. In otherwords, the user may press a switch or a button, as soon as the userobserves any object extending within the exclusion zone. In response,the controller 108 directs the robotic system to interrupt any furthermovement of the arm assembly 112 (and hence of the emission head 105mounted at the distal end 113 thereof) toward the exclusion zone 140.

Alternatively, the collision avoidance subsystem 200 may be anautomatically activated system, in which the interception of any objectextending within the exclusion zone 140 automatically triggers ashut-off response by the controller 108. The shut-off response preventsany further motion of the arm assembly 112 toward the exclusion zone140.

In another embodiment, illustrated in FIG. 3B, a light source may befixedly positioned with respect to the emission head 105 of the x-raylinac 104. For example, a light source may be mounted at the distal end113 of the arm assembly 112, next to the x-ray linac 104. In thisembodiment, the light source defines an exclusive zone that “travels”with the bead.

By way of example, a rectangular exclusion zone 140 may be defined whichis attached to, and travels with, the head 113, as illustrated in FIG.3B. In the illustrated exemplary embodiment, the exclusion zone 140 isdefined by four distinct planar light beams 250A, 250B, 250C, and 250D,each extending parallel to a beam axis 121 from a respective one of linesources 260A, 260B, 260C, and 260D. The planar beams 250A, 250B, 250C,and 250D together define a rectangular cross-section parallelepipedexclusion zone 140 extending along a beam axis 121. The exclusion zone140 is defined by a number of planar barriers, defined by the planarlight beams 250A-250D. As in the exclusion zone 140 described inconjunction with FIG. 3A, each of the beams 250A, 250B, 250C, and 250Dmay for example be formed from a linear array of light sources (such aslasers or LEDs), or from a swept single light source.

In one exemplary embodiment of the invention, the exclusion zone 140 isnot a static zone, but rather is a variable dimension zone. In otherwords, the exclusion zone is defined by boundaries that are movable, andthe dimensions of the exclusion zone 140 can be modified in near realtime. In this embodiment, one or more barriers defining an exclusionzone may be selectively disabled, e.g. in a planar dimension. Forexample, one or more planar barriers defining the exclusion zone 140 maybe selectively disabled, thereby changing the dimensions of theexclusion zone 140.

FIG. 4 illustrates a collision avoidance subsystem 300, constructed inaccordance with another embodiment of the present invention, andincluding an array 310 of acoustic transducers 320. In the illustratedembodiment, the exclusion zone 140 is implemented via the array ofacoustic transducers 320. The transducers 320 are capable of determiningthe distance to the nearest object, preferably at 6 to 80 inchestherefrom. In one form, the transducers 320 ping to determined thedistance to the nearest object. The acoustic transducers 320 may beultrasonic transducers, by way of example.

In the illustrated embodiment, the array 310 of acoustic transducers 320is fixedly coupled to the x-ray emission head of the linac 104. Each ofthe transducers 320 transmits a succession of acoustic pulses 322 alonga transmission axis 330 extending from the linac 104. Each transducerdetects acoustic energy back-scattered along the transmission axis 330from any object disposed along the transmission axis. The subsystem 300includes software for mutually aligning the beam axes (prior tooperation of the subsystem 300)t whereby cross-sections of adjacentpairs of pulses 322 transverse to the transmission axis 330 arecontiguous at a predetermined distance from the head 105 to minimizegaps in the covered area.

The collision avoidance subsystem 300 includes software 301 fordetermining, from the received back-scattered acoustic energy, thedistance between the linac and the object. In response to the determineddistance being at or less than a predetermined value, the software sendssignals to the controller 108 t instructing the controller to interruptany further motion of the head 105 toward the exclusion zone 140.

In an exemplary embodiment, an array of four ultrasonic transducers 320are arranged about the base of the linac 104 in a rectangular pattern,as shown in FIG. 5A. In addition, the acoustic pulses 322 form a sensecone 340, as illustrated in FIGS. 5A and 58.

In the embodiment illustrated in FIG. 5C, the four ultrasonic sensors320 are arranged around the housing of the collimator 107, so as toprovide full coverage of the collimator at 24 inches. In particular, twoof the sensors 320 are mounted on a base plate 360 of the linac 104, viaexisting holes 361 in the base plate 360. Two sensors are mounted on thecover 380 of the linac 104. The cover thus includes three holes that arecut therein, two holes 381 for the sensors and one hole 382 for wireexit.

Each ultrasonic sensor 320 determines the distance from the nearestobject, when such distance ranges from 6 to 80 inches. Each sensorreports an analog voltage value corresponding to the sensed distance,ranging from 0 to 10 volts: 0 volts indicates 6 inches to the nearestobject, whereas 10 volts indicates 80 inches to the nearest object. Eachsensor pings at 150 KHz, with a response time of 25 milliseconds, and isable to discern objects at plus or minus 10 degrees from theperpendicular view angle. Before operation, the input of all foursensors 320 are synchronized, in order to prevent crosstalk between thesensors. The sensors 320 may be connected to the analog input on therobot 102. In one form, the sensors may be manually disabled by aswitch.

FIG. 6 illustrates a collision avoidance subsystem 400, constructed inaccordance with another embodiment of the present invention, andincluding a tactile sensor. In the embodiment illustrated in FIG. 6, thepresent invention implements the exclusion zone 140 with a sensor 430,which generates an indicative signal if and when it impacts with anobject in the exclusion zone 140. In the illustrated embodiment, thesensor 430 is a tactile sensor, such as a pressure-sensitive pad;however, other types of sensors (including but not limited to infraredsensors and electrostatic capacitance sensors) may be used in otherembodiments of the invention.

The tactile sensor 430 is disposed on a surface 422 of the articulatedarm assembly 112 of the robot 102. The sensor 430 is operative togenerate an alarm signal upon impact of sensor 430 with any object,during motion of the arm 112 and/or head

105. In a particular, in the illustrated embodiment the tactile sensor430 includes a fluid-filled bladder 432, and a pressure transducer 434coup]ed to the bladder 432 for generating the alarm signal, when fluidpressure in the bladder 432 exceeds a predetermined threshold. Thecontroller 108 includes software, responsive to the alarm signal, forsending instructions to the robot to interrupt any further motion of thearm 112 and/or head 105.

The collision avoidance subsystems, described in the embodimentsillustrated in FIGS. 4-6, may include software filters on the returnsignal, for minimizing false positive signals.

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A method, comprising: calculating a variable dimension exclusion zoneof a radiosurgery system, the radiosurgery system comprising an x-raysource having an emission head and an arm assembly; and preventing atleast one of the emission head or arm assembly from entering thevariable dimension exclusion zone.
 2. The method of claim 1, whereincalculating the variable dimension exclusion zone comprises defining oneor more moveable boundaries as dimensions of the variable dimensionexclusion zone.
 3. The method of claim 2, further comprising changingthe dimensions of the variable dimension exclusion zone.
 4. The methodof claim 3, wherein changing the dimensions of the variable dimensionexclusion zone comprises selectively disabling one or more moveableboundaries of the variable dimension exclusion zone.
 5. The method ofclaim 3, wherein the one or more moveable boundaries are planar barrier,and wherein changing the dimensions of the variable dimension exclusionzone comprises selectively disabling one or more planar barriers.
 6. Themethod of claim 2, further comprising modifying the dimensions of thevariable dimension exclusion zone during treatment.
 7. The method ofclaim 6, wherein modifying the dimensions of the variable dimensionexclusion zone comprises receiving feedback information from a patientpositioning system.
 8. The method of claim 6, wherein modifying thedimensions of the variable dimension exclusion zone comprises receivingfeedback information from a controller of a radiosurgery system.
 9. Themethod of claim 1, wherein preventing at least one of the emission heador arm assembly from entering the variable dimension exclusion zonecomprises stopping any further motion of the at least one of emissionhead or arm assembly when the at least one of emission head or armassembly reaches a boundary of the variable dimension exclusion zone.10. The method of claim 1, wherein preventing the at least one ofemission head or arm assembly from entering the variable dimensionexclusion zone comprises: calculating an additional exclusion zone,wherein the additional exclusion zone is a first layer and the exclusionzone is a second layer, wherein the first layer is outside the secondlayer; and slowing down motion of the at least one of emission head orarm assembly upon reaching a boundary of the additional exclusion zone.11. A method, comprising: establishing a exclusion zone of aradiosurgery system, the radiosurgery system comprising an x-ray sourcehaving an emission head; moving the emission head during treatment of apatient, wherein the exclusion zone travels with the emission head; anddetecting a presence and location of an object in the travelingexclusion zone.
 12. The method of claim 11, wherein the radiosurgerysystem comprises an arm assembly coupled to the x-ray source having theemission head, and wherein the exclusion zone travels with the armassembly.
 13. The method of claim 11, wherein the object comprises apart of the radiosurgery system.
 14. The method of claim 11, wherein theobject comprises a part of the patient.
 15. The method of claim 11,wherein the object comprises a part of an equipment in a treatment roomin which the radiosurgery system resides.
 16. The method of claim 11,further comprising preventing the emission head from effecting acollision with the object in the traveling exclusion zone.
 17. Themethod of claim 13, wherein preventing the emission head from effectingthe collision comprises: detecting an intrusion of the object into thetraveling exclusion zone; and preventing or slowing down furtherrelative advance of the object in the traveling exclusion zone.
 18. Themethod of claim 13, wherein preventing the emission head from effectingthe collision comprises: detecting an intrusion of the object into thetraveling exclusion zone; and preventing or slowing down furtherrelative advance of the object in the traveling exclusion zone.
 19. Themethod of claim 17, wherein detecting the intrusion of the objectcomprises using at least one of a laser rangefinder, one or more opticalemitter-receiver pairs, an array of acoustic transducers, a capacitancesensor, or an infrared sensor to detect the intrusion of the object. 20.An apparatus, comprising: a radiosurgery system comprising an x-raysource having an emission head and an arm assembly; and a controllercoupled to the radiosurgery system, the controller to calculate avariable dimension exclusion zone of a radiosurgery system, wherein thecontroller is configured to prevent at least one of the emission head orarm assembly from entering the variable dimension exclusion zone. 21.The apparatus of claim 20, wherein the controller is configured todefine one or more moveable boundaries as dimensions of the variabledimension exclusion zone, and wherein the controller is configured tochange the dimensions of the variable dimension exclusion zone.
 22. Theapparatus of claim 20, wherein the controller is configured to defineone or more moveable boundaries as dimensions of the variable dimensionexclusion zone, and wherein the controller is configured selectivelydisable one or more moveable boundaries of the variable dimensionexclusion zone.
 23. An apparatus, comprising: a radiosurgery systemcomprising an x-ray source having an emission head and an arm assembly;and means for calculating a variable dimension exclusion zone of aradiosurgery system.
 24. The apparatus of claim 23, further comprisingmeans for preventing at least one of the emission head or arm assemblyfrom entering the variable dimension exclusion zone.
 25. The apparatusof claim 23, further comprising means for changing the dimensions of thevariable dimension exclusion zone.
 26. An apparatus, comprising: meansfor establishing a exclusion zone of a radiosurgery system, theradiosurgery system comprising an x-ray source having an emission head;means for moving the emission head during treatment of a patient,wherein the exclusion zone travels with the emission head; and means fordetecting a presence and location of an object in the travelingexclusion zone.
 27. The apparatus of claim 26, further comprising meansfor preventing the emission head from effecting a collision with theobject in the traveling exclusion zone.
 28. The apparatus of claim 26,further comprising: means for detecting an intrusion of the object intothe traveling exclusion zone; and means for preventing or slowing downfurther relative advance of the object in the traveling exclusion zone.